Such force-transmitting arrangements are known to someone skilled in the art of valve controllers with hydraulic valve play compensation and are embodied according to the architecture of the internal-combustion engine. Thus, for the so-called “Overhead Camshaft” valve train construction also known as “OHC” with a camshaft arranged in the cylinder head, for the most part bucket tappets, rocker arms or finger levers, and also stationary pivot bearings for pivot levers are used, each with hydraulic valve play compensation.
In addition, such force-transmitting arrangements also find multipurpose use in the so-called “Overhead Valve” valve train arrangement also known in short as “OHV” predominantly for large-volume internal-combustion engines embodied as V engines. In the OHV arrangement, the valve train is characterized by a camshaft, which is supported in the engine block of the internal-combustion engine in the vicinity of the crankshaft and whose cam lobes are picked up by tappets as force-transmitting arrangements, which can move in the longitudinal direction and which are usually equipped with hydraulic valve play compensation, and are transformed into a stroke movement of each tappet which contacts the cam. The stroke movement of the tappet is typically transmitted to one or more gas-exchange valves allocated to the tappet via a tappet push rod, which activates a rocker arm supported in the cylinder head of the internal-combustion engine.
The known advantages of a hydraulic and thus automatic valve play compensation device includes, in particular, the elimination of the valve play adjustment at the initial assembly and service of the internal-combustion engine, its quiet running, and favorable exhaust-gas emission behavior. However, these advantages can be realized completely only under the assumption that the hydraulic valve play compensation device is functional or ready to function in all operating states, including standstill and starting of the internal-combustion engine. The essential basis for this obviously consists in a suitable supply of hydraulic medium to the valve play compensation device. For this purpose, the hydraulic medium is fed during the operation of the internal-combustion engine by a hydraulic-medium pump via supply lines to a compensation piston of the valve play compensation device, wherein the compensation piston borders a hydraulic pad used for transferring movement or force in a working space. The working space has a variable volume, because the compensation piston is always striving to adjust the height of the hydraulic pad enclosed by the working space, so that mechanical play in the valve train is eliminated during the stroke-free base circle phase of the cam. The compensation piston is typically formed with a hollow cylindrical shape and encloses a hydraulic medium reservoir, which supplies the working space with hydraulic medium by means of a non-return valve during valve play compensation movements, i.e., for an expanding working space. Here, it has proved to be useful that the volume of the hydraulic medium reservoir equals a multiple of the volume of the working space, in order to reliably exclude undesired suctioning of air or gas bubbles into the working space under all operating conditions of the internal-combustion engine.
A starting process of a cold internal-combustion engine represents an especially critical operating state in this condition, wherein the engine typically was turned off with one or more open gas-exchange valves, so that the compensation pistons of the associated valve play compensation devices have descended partially or completely due to extensive displacement of hydraulic medium from the working space due to the force effect of the gas-exchange valve spring and after a period of temporary standstill phase of the internal-combustion engine. In addition, during the starting process the hydraulic medium pump does not deliver any or a sufficient hydraulic medium volume flow to the compensation piston. In this respect, it is essentially the only task of the hydraulic medium reservoir to completely cover the considerable need for hydraulic medium of the working space during its expansion from the descended position of the compensation piston in its working position. An insufficiently large or an insufficiently filled hydraulic medium reservoir would inevitably lead to suctioning of air or gas bubbles into the working space. The consequences of a working space containing air or gas bubbles are known to someone skilled in the art and are perceived audibly and disruptively as so-called valve tapping primarily due to high contact speeds of the gas-exchange valve during its closing process.
The requirement for a sufficiently large hydraulic medium reservoir is increasingly in conflict with the goal of further reducing the installation space and/or the mass of the force-transmitting arrangement or for expanding the functionality of the force-transmitting arrangement for an unchanged installation space. The latter case includes, in particular, variable force-transmitting arrangements, which are formed as switchable cam followers and can transfer the strokes of various cams selectively to the gas-exchange valve according to the switching state of their coupling means and/or can completely cancel out the stroke of a cam. Thus, it is typical, for example, in switchable tappet push rod valve trains with an OHV arrangement to nest cam follower parts, which can move longitudinally relative to each other and which can be coupled to each other, so that the outer and attachment geometry of the cam follower can remain essentially unchanged. However, this usually requires a reduction in installation space of the hydraulic valve play compensation device and consequently a volume reduction of the hydraulic medium reservoir enclosed by the compensation piston with the previously mentioned risk and consequences of a lack of hydraulic medium supply to the working space.
This problem is often intensified in that the force transmitting arrangement and with it the compensation piston together with the hydraulic medium reservoir are installed in the internal-combustion engine at an angle to the force of gravity. This can lead to a significant loss of hydraulic medium from the hydraulic medium reservoir, which also endangers successful refilling of the working space, because the hydraulic medium can return via supply openings from the hydraulic medium reservoir into the hydraulic medium supply.
In the state of the art, there are already approaches to solving this intensification of the problem mentioned above. For example, in U.S. Pat. No. 2,688,319, in U.S. Pat. No. 4,462,364, and also in DE 197 54 016 A1, limiting means are proposed, which are supposed to prevent draining of the hydraulic medium reservoir. However, these limiting means are all arranged in the immediate area of the compensation piston and consequently can guarantee at most a filling level corresponding to the hydraulic medium reservoir enclosed directly by the compensation piston. Consequently, it can be necessary, especially for switchable cam followers with reduced installation space compensation pistons, to expand the then insufficiently large hydraulic medium reservoir by cavities located outside the compensation piston. In this case, the limiting means of the cited documents are unsuitable, because they cannot prevent return of hydraulic medium located outside of the compensation piston.